Java applications are complied to bytecode then JIT and JVM takes care of code execution. Here you will find some insights about how JIT compiler works.

I am guessing that many of you use Java as your primary language in your day-to-day work. Have you ever thought about why HotSpot is even called HotSpot or what the Tiered Compilation is and how it relates to Java? I will answer these questions and a few others through the course of this article. I will begin this by explaining a few things about compilation itself and the theory behind it.

Turning Source Code to Machine Code

In general, we can differentiate two basic ways of translating human readable code to instructions that can be understood by our computers:

Static (native, AOT) Compilation

• After code is written, a compiler will take it and produce a binary executable file. This file will contain set of machine code instructions targeted for particular CPU architecture. Of course the same binary should be able to run on CPUs with similar set of instructions but in more complex cases your binary may fail to run and may require recompiling to meet server requirements. We lose the ability to run on multiple platforms for the benefit of faster execution on a dedicated platform.

Interpretation

• Already existing source code will be run and turned into binary code line by line by the interpreter while the exact line is being executed. Thanks to this feature, the application may run on every CPU that has the correct interpreter. On the other hand, it will make the execution slower than in the case of statically compiled languages. We benefit from the ability to run on multiple platforms but lose on execution time.

As you can see both types have their advantages and disadvantages and are dedicated to specific use cases and will probably fail if not used in the correct case. You may ask – if there are only two ways does it mean that Java is an interpreted or a statically compiled language?

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